Development of Respiratory System PDF

MD2 Anatomy & Neurobiology Anatomy II Development of respiratory system By Dr Hasan Reda Elsayed Associate Professor of Anatomy & Embryology in College of Medicine, National University, Oman, and Mansoura University, Egypt ...

MD2 Anatomy & Neurobiology Anatomy II Development of respiratory system By Dr Hasan Reda Elsayed Associate Professor of Anatomy & Embryology in College of Medicine, National University, Oman, and Mansoura University, Egypt  SLOs SLO# 1 : Explain the formation of the respiratory diverticulum SLO# 2 : Describe the development of larynx and its congenital anomalies SLO# 3 : Describe the development of the trachea SLO# 4 : Explain the embryological basis of tracheo-esophageal fistula SLO# 5 : Describe the development of the bronchial bud and its derivatives SLO# 6 : Describe the stages of lung development & its main events SLO# 7 : Describe the congenital anomalies of lung development SLO# 8 : Describe the formation of the pleura Intro to respiratory system  Development of respiratory diverticulum Time: During the 4th week of development Molecular regulation: via an increase in retinoic acid secreted by surrounding mesoderm. Origin: Respiratory diverticulum develops from Ventral wall of the cranial part of foregut The lining epithelium of the respiratory tract is endodermal (except that of nose is ectodermal)  Development of respiratory diverticulum Other coats of respiratory system (smooth muscles, cartilages, connective tissue, vessels) develop from splanchnic lateral plate mesoderm around lung buds. Neural crest cells share in formation of laryngeal cartilages + ganglia & nerves supplying respiratory system  Development of respiratory diverticulum Cranial part of foregut then has 2 parts: 1. Dorsal part forms: pharynx & esophagus. 2. Ventral part forms: larynx & trachea.  Development of respiratory diverticulum Pharynx & larynx are still connected by a laryngeal orifice to allow air entry from pharynx to larynx then to trachea. While Trachea & oesophagus is separated  Development of respiratory diverticulum Trachea & oesophagus is separated by tracheoesophageal folds that form a septum. Respiratory diverticulum grows caudally to give larynx, trachea & divides into 2 lung buds.  Development of respiratory diverticulum The lining epithelium of respiratory tract proliferates causing obliteration of the tract, followed by recanalization. The recanalization of larynx causes development of true and false vocal folds and laryngeal ventricle in between  Anomalies of larynx Laryngeal atresia: due to failed recanalization Laryngeal web: between vocal folds due to incomplete canalization Laryngomalacia: ❖ is the most common cause of infantile chronic stridor (airway obstruction) ❖ cause: the soft, immature cartilage of larynx collapses inward during inhalation Anomalies of Trachea Tracheal atresia: Tracheal stenosis: Tracheal diverticulum: Tracheomalacia: Soft tracheal cartilages partly collapse especially during increased airflow.  Anomalies of trachea Tracheo- esophageal fistula (TEF): 1:3000 birth ▪ Results from abnormal partitioning of cranial foregut by tracheoesophageal septum. ▪ Neonates may be born preterm d.t. polyhydramnios caused by the associated esophageal atresia ▪ Neonates may present with choking after breast feeding and may be pneumonia. ▪ It may be associated with other anomalies e.g. cardiac abnormalities, in 33% of these cases. ▪ TEF is a component of VACTERL association (vertebral anomalies, anal atresia, cardiac defects, tracheoesophageal fistula, esophageal atresia, renal anomalies, and limb defects)  Anomalies of Trachea Tracheo- esophageal fistula (TEF): Variants of TEF: A. Upper esophagus ends in a blind pouch and the lower segment forms a fistula with trachea. This is the most frequent variant (90% of cases). B. Isolated esophageal atresia. C. H-type TEF. D,E. Other variations.  Development of Bronchial tree Stems of lung buds form right & left main (primary) bronchi. The right gives 3 lobar (secondary) bronchi while the left gives 2 (following the number of lung lobes) The right lobar bronchi give 10 segmental (tertiary) bronchi, while (8-10) in left (following the number of lung segments) 17 generations of subdivisions occur before birth. 6 more generations are formed after birth till 10y Fibroblast growth factor guides the branching  Stages of lung maturation Stage Time Characters Pseudo- 5-16 w Terminal bronchioles are formed. glandular Canalicular 16-26 w Respiratory bronchioles and alveolar ducts are formed Terminal 26w-birth Primitive alveoli are formed sac Alveolar 8m- 1. Alveoli increase in number, childhood 2. Their lining pneumocyte Type I becomes flattened 3. Alveoli develop more mature contact with capillaries to form (Blood-air barrier) 4. Pneumocyte type II develops and secretes surfactant (phospholipid-rich & lowers the surface tension of alveoli). It increases in week 34 and maximum at last 2 weeks NB: Breathing signals before birth causes amniotic to be inhaled into lung followed by expelling of surfactant into amniotic fluid, that later becomes engulfed by macrophages causing maternal immunity reaction involving prostaglandins secretion and thus initiating uterine contraction and labour Anomalies of lung Respiratory distress syndrome: (Hyaline membrane disease): ❖ It affects 1% of newborns ❖ It is the cause of 20% of deaths among newborn ❖ Due to insufficient surfactant production specially in premature infants ❖ Collapse of alveoli with failure of alveoli to ventilate adequately ❖ Alveoli contain fluid of high protein content resembling a hyaline membrane Anomalies of lung ❑ Lung agenesis or hypoplasia ❑ Ectopic lung lobe: Arising as an additional respiratory bud from trachea or esophagus ❑ Supernumerary lobules: may cause unexpected difficulties during bronchoscopy ❑ Congenital cysts of lung: dilated terminal bronchioles (if multiple may cause Honey comb-appearance on radiograph)  Development of pleura ▪ Lung buds expand into primitive pleurae (=pericardio-peritoneal canals) (middle parts of intraembryonic coelom) ▪ Pleuroperitoneal & pleuropericardial folds separate primitive pleural cavities from peritoneal & pericardial cavities.  Development of pleura Splanchnic lateral plate mesoderm which covers lung ➔ visceral pleura. Somatic lateral plate mesoderm which lines body wall ➔ parietal pleura. The space between parietal & visceral pleura containing intraembryonic coelom ➔ pleural cavity. Thank you